The present invention relates to 3-fluoro-2-oxobicyclo[3.1.0]hex-3-ene-6-carboxylic acid derivatives and a process for producing the same, and a process for producing a fluorine-containing amino acid derivative (2-amino-3-fluorobicyclo[3.1.0]hexane-2,6-dicarboxylic acid).
In recent years, with the repeated cloning of glutamate receptor genes, it has become clear that there are surprisingly many subtypes of glutamate receptors. At present, glutamate receptors are roughly classified into two types: the xe2x80x9cionotropic typexe2x80x9d, in which the receptor has an ion channel type structure, and the xe2x80x9cmetabotropic typexe2x80x9d, in which the receptor is coupled to G-proteins. Ionotropic receptors are classified pharmacologically into three types: N-methyl-D-aspartic acid (NMDA), xcex1-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA), and kainate (Science, 258, 597-603, 1992). Metabotropic receptors are classified into eight types, type 1 through type 8 (J. Neurosci., 13, 1372-1378, 1993; Neuropharmacol., 34, 1-26, 1995).
The metabotropic glutamate receptors are classified pharmacologically into three groups. Of these, group 2 (mGluR2/mGluR3) bind with adenylcyclase, and inhibit the accumulation of the Forskolin stimulation of cyclic adenosine monophosphate (cAMP) (Trends Pharmacol. Sci., 14, 13 (1993)), and for this reason, it is suggested that the compounds acting on group 2 metabotropic glutamate receptors have treatment effects and prevention effects on psychiatric disorders such as, for example, schizophrenia, anxiety and its associated diseases, depression, bipolar disorder and epilepsy; and neurological diseases such as drug dependence, cognitive disorders, Alzheimer""s disease, Huntington""s chorea, Parkinson""s disease, dyskinesia associated with muscular stiffness, cerebral ischemia, cerebral failure, myelopathy, and head trauma.
In addition, in PCT/JP99/00324 which is the International Patent Application by the present applicant, 2-amino-3-fluorobicyclo[3.1.0]hexane-2,6-dicarboxylic acid as a compound acting on group 2 metabotropic glutamate receptors is disclosed. Furthermore, in the specification of the same, a preparation method thereof as described below, which comprises steps of subjecting an (1S, 5R, 6S)- or (1SR, 5RS, 6SR)-2-oxobicyclo[3.1.0]hexane-6-carboxylic acid derivative (8) to fluorination, and then, hydantoination, followed by hydrolysis, is proposed. 
Heretofore, no synthesis methods of 2-amino-3-fluorobicyclo[3.1.0]hexane-2,6-dicarboxylic acid, other than that of the synthesis schemes described above, have been reported.
An object of the present invention is to provide a process for further efficiently producing a fluorine-containing amino acid derivative (2-amino-3-fluorobicyclo[3.1.0]hexane-2,6-dicarboxylic acid) acting on group 2 metabotropic glutamate receptors, which has treatment effects and prevention effects on psychiatric disorders such as schizophrenia, anxiety and its associated diseases, depression, bipolar disorder, and epilepsy, and neurological diseases such as drug dependence, cognitive disorders, Alzheimer""s disease, Huntington""s chorea, Parkinson""s disease, dyskinesia associated with muscular stiffness, cerebral ischemia, cerebral failure, myelopathy, and head trauma, as well as novel intermediates which are useful for said production process, and a process for producing the intermediates.
After conducting diligent research with regard to a process for producing a fluorine-containing amino acid derivative [(1S, 2S, 3S, 5R, 6S)- or (1SR, 2SR, 3SR, 5RS, 6SR)-2-amino-3-fluorobicyclo[3.1.0]hexane-2, 6-dicarboxylic acid], the present inventors discovered a process for efficiently producing the same, which to employ an (1S, 5R, 6S)- or (1SR, 5RS, 6SR)-2-oxobicyclo[3.1.0]hex-3-ene-6-carboxylic acid derivative as a starting material, via an (1S, 5R, 6S)- or (1SR, 5RS, 6SR)-3-fluoro-2-oxobicyclo[3.1.0]hex-3-ene-6-carboxylic acid derivative which is a novel intermediate, consequently completed the present invention.
That is, the present invention corresponds to a 3-fluoro-2-oxobicyclo[3.1.0]hex-3-ene-6-carboxylic acid derivative represented by Formula (1): 
[in the formula, R represents OR1 or NR1R2, wherein R1 and R2 are identical or different, and each represents a hydrogen atom, a C1-C6 alkyl group, a C3-C6 cycloalkyl group, a (C3-C6 cycloalkyl) (C1-C6 alkyl) group, an aryl group, an aryl (C1-C6 alkyl) group, a (C1-C6 alkoxy) (C1-C6 alkyl) group, a C1-C6 hydroxyalkyl group, a (C1-C6 alkylthio) (C1-C6 alkyl) group, or a C1-C6 mercaptoalkyl group], and a process for producing the derivative of Formula (1), characterized in that the process comprises the steps of:
oxidizing an (1S, 5R, 6S)- or (1SR, 5RS, 6SR)-2-oxobicyclo[3.1.0]hex-3-ene-6-carboxylic acid derivative represented by Formula (2): 
xe2x80x83[in the formula, R is the same as described above] by means of a peroxide, to produce an (1S, 3R, 4R, 5R, 6S)- or (1SR, 3RS, 4RS, 5RS, 6SR)-epoxy derivative represented by Formula (3): 
xe2x80x83[in the formula, R is the same as described above]; and reacting said epoxy derivative with a fluorination agent, and a process for producing (1S, 2S, 3S, 5R, 6S)- or (1SR, 2SR, 3SR, 5RS, 6SR)-2-amino-3-fluorobicyclo[3.1.0]hexane-2,6-dicarboxylic acid represented by Formula (7): 
xe2x80x83a pharmaceutically acceptable salt thereof, or a hydrate thereof, characterized in that the process comprises the steps of:
hydrogenating the derivative represented by Formula (1), to produce an (1S, 3S, 5R, 6S)- or (1SR, 3SR, 5RS, 6SR)-3-fluoro-2-oxobicyclo[3.1.0]hexane-6-carboxylic acid derivative represented by Formula (4): 
xe2x80x83[in the formula, R is the same as described above];
subjecting the same to hydantoination or aminocyanidation, to produce an (1S, 2S, 3S, 5R, 6S)- or (1SR, 2SR, 3SR, 5RS, 6SR)-hydantoin derivative represented by Formula (5): 
xe2x80x83[in the formula, R is the same as described above], or an (1S, 2S, 3S, 5R, 6S)- or (1SR, 2SR, 3SR, 5RS, 6SR)-aminocyanide derivative represented by Formula (6): 
xe2x80x83[in the formula, R is the same as described above]; and
subjecting them to a hydrolysis.
The terms used in the present invention are defined in the following. In the present invention, xe2x80x9cCn-Cmxe2x80x9d means that the group following the xe2x80x9cCn-Cmxe2x80x9d has from n to m carbon atoms.
The C1-C6 alkyl group means a straight-chain or branched-chain alkyl group having 1 to 6 carbon atoms, examples of which include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a t-butyl group, a pentyl group, an isopentyl group, a hexyl group, an isohexyl group, and the like.
The C3-C6 cycloalkyl group means a cyclic alkyl group having 3 to 6 carbon atoms, including, for example, a cyclopropyl group, a cyclopentyl group, a cyclohexyl group, or the like.
The (C3-C6 cycloalkyl) (C1-C6 alkyl) group means a group having a form mixed with a C3-C6 cycloalkyl group and a C1-C6 alkyl group, examples of which include a cyclopropylmethyl group, a cyclobutylmethyl group, a cyclopentylmethyl group, a cyclohexylmethyl group, and the like.
The aryl group means a phenyl group, a naphthyl group, or the like, and is preferably a phenyl group. The aryl (C1-C6 alkyl) means a straight-chain or branched-chain alkyl group having 1 to 6 carbon atoms, substituted with at least one aryl group, and preferably a phenyl group. Examples thereof include, for example, a benzyl group, a diphenylmethyl group, a 1-phenylethyl group, a 2-phenylethyl group, and the like.
The (C1-C6 alkoxy) (C1-C6 alkyl) group means a group having a form mixed with a C1-6 alkoxy group and a C1-6 alkyl group. The C1-C6 alkoxy group means a straight-chain or branched-chain alkoxy group having 1 to 6 carbon atoms, including, for example, a methoxy group, an ethoxy group, a propoxy group, an isopropoxy group, a butoxy group, an isobutoxy group, a t-butoxy group, a pentyloxy group, an isopentyloxy group, or the like. Therefore, examples of the (C1-C6 alkoxy) (C1-C6 alkyl) groups include a methoxyethyl group, an ethoxyethyl group, a propoxyethyl group, an isopropoxyethyl group, a butoxyethyl group, an isobutoxyethyl group, a pentyloxyethyl group, an isopentyloxyethyl group, and the like.
The C1-C6 hydroxyalkyl group means a C1-6 alkyl group substituted with at least one hydroxyl group. Therefore, examples of the C1-C6 hydroxyalkyl group include a 2-hydroxyethyl group, a 3-hydroxypropyl group, a 2,3-dihydroxypropyl group, and the like.
The (C1-C6 alkylthio) (C1-C6 alkyl) group means a group having a form mixed with a C1-C6 alkylthio group and a C1-C6 alkyl group. The C1-C6 alkylthio group means a straight-chain or branched-chain alkylthio group having 1 to 6 carbon atoms, including, for example, a methylthio group, an ethylthio group, a propylthio group, an isopropylthio group, a butylthio group, an isobutylthio group, a t-butylthio group, a pentylthio group, an isopentylthio group, and the like. Therefore, examples of the (C1-C6 alkylthio) (C1-C6 alkyl) group include a methylthiomethyl group, a 2-methylthioethyl group, and the like.
The C1-C6 mercaptoalkyl group means a C1-C6 alkyl group substituted with at least one mercapto group. Therefore, examples of the C1-C6 mercaptoalkyl group include a 2-mercaptoethyl group, a 3-mercaptopropyl group, a 2,3-dimercaptopropyl group, and the like.
In each group described above, at least one hydrogen atom on the group may be substituted with an atom or a group, which is not hydrogen, for example, a halogen atom such as a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom; a nitro group; an amino group; a hydroxyl group; a thiol group; a formyl group; a carboxyl group; a cyano group; a carbamoyl group; an alkyl group such as a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a sec-butyl group, tert-butyl group, a pentyl group, an isopentyl group, a neopentyl group, or a tert-pentyl group; an aryl group and a heterocyclic group such as a phenyl group, a naphthyl group, a biphenyl group, an anthranyl group, a pyrrolyl group, a pyridyl group, or a thienyl group; an alkoxycarbonyl group such as a methoxycarbonyl group, or an ethoxycarbonyl group; an acyl group such as an acetyl group, or a benzoyl group; an alkoxy group such as a methoxy group, an ethoxy group, or a propoxy group; or an alkylthio group such as a methylthio group, an ethylthio group, or a propylthio group. Therefore, for example, a 2,2,2-trichloroethyl group, a phenacyl group, a 2,6-dimethylcyclohexyl group, and a 4-methoxybenzyl group, and the like are included in a scope of R1 and R2. The number of the carbon atoms in these substituents is not included in the numbers n or m described above.
In addition, the pharmaceutically-acceptable salt in the present invention refers to, for example, a salt with an inorganic acid such as sulfuric acid, hydrogen chloride, or phosphoric acid; a salt with an organic acid such as acetic acid, oxalic acid, lactic acid, tartaric acid, fumaric acid, maleic acid, methanesulfonic acid, or benzenesulfonic acid; a salt with an amine such as trimethylamine, or methylamine; or a salt with a metal ion such as sodium ion, potassium ion, or calcium ion.
The compounds represented by Formulae (1) to (7) may be produced according to the synthetic methods described below (in the following reaction scheme, R represents the same substituent as described above). 
Step A: (1S, 5R, 6S)- or (1SR, 5RS, 6SR)-2-oxobicyclo[3.1.0]hex-3-ene-6-carboxylic acid derivative. (2) (in the following, referred to as xe2x80x9cenone derivative (2)xe2x80x9d) is reacted with a peroxide in an inert solvent at a reaction temperature ranging from xe2x88x9230xc2x0 C. to 150xc2x0 C., and preferably from 0xc2x0 C. to 50xc2x0 C., to produce an epoxy derivative (3).
In this step, as examples of the inert solvent, mention may be made of, for example, alcohols such as methanol, ethanol, isopropyl alcohol, or ethylene glycol; ethers such as diethyl ether, tetrahydrofuran, dioxane, or 1,2-dimethoxyethane; hydrocarbons such as benzene or toluene; amides such as N,N-dimethylformamide; ketones such as acetone or ethyl methyl ketone; acetonitrile; water; acetic acid; trifluoroacetic acid; a mixture of these solvents; or the like. Examples of the peroxide include, for example, a peroxide of an organic carboxylic acid such as m-chloroperbenzoic acid or peracetic acid; a peroxide of an alcohol such as tert-butylhydroperoxide; hydrogen peroxide; and the like.
Step B: The epoxy derivative (3) is reacted with a fluorination agent in an inert solvent at a reaction temperature ranging from xe2x88x9230xc2x0 C. to 200xc2x0 C., and preferably from 0xc2x0 C. to 150xc2x0 C., to synthesize 3-fluoro-2-oxobicyclo[3.1.0]hex-3-ene-6-carboxylic acid derivative (1) which corresponds to the compound according to the present invention.
In this step, as examples of the inert solvent, mention maybe made of, for example, alcohols such as methanol, ethanol, isopropyl alcohol, or ethylene glycol; ethers such as diethyl ether, tetrahydrofuran, dioxane, or 1,2-dimethoxyethane; hydrocarbons such as benzene or toluene; amides such as N,N-dimethylformamide; or a mixture of these solvents. Examples of the fluorination agent include, for example, fluorine; hydrogen fluoride; an inorganic fluorinated compound such as potassium hydrogenfluoride (HKF2); a quaternary ammonium fluorinated compound such as tetrabutylammonium fluoride; an N-fluoro-type fluorinated compound such as N-fluoropyridinium triflate, N-fluoro-N-t-butylbenzenesulfonamide, N-fluorosaccharinsultam, N-fluorobis(benzenesulfone)imide, N-fluoro-o-benzenesulfonimide; ClO3F; CF3COOF; and the like.
Step C: 3-Fluoro-2-oxobicyclo[3.1.0]hex-3-ene-6-carboxylic acid derivative (1) is hydrogenated in an inert solvent at a reaction temperature ranging from xe2x88x9230xc2x0 C. to 100xc2x0 C., and preferably from 0xc2x0 C. to 50xc2x0 C., to guide it to (1S, 3S, 5R, 6S)-or (1SR, 3SR, 5RS, 6SR)-3-fluoro-2-oxobicyclo[3.1.0]hexane-6-carboxylic acid derivative (4) (in the following, referred to as xe2x80x9cfluoroketone derivative (4)xe2x80x9d).
In this step, as examples of the inert solvent, mention may be made of, for example, alcohols such as methanol, ethanol, isopropyl alcohol, or ethylene glycol; ethers such as diethyl ether, tetrahydrofuran, dioxane, or 1,2-dimethoxyethane; hydrocarbons such as benzene or toluene; amides such as N,N-dimethylformamide; water; or a mixture of these solvents. As the hydrogenation catalyst, a metal which is commonly employed as a hydrogenation catalyst, such as palladium/activated carbon, palladium black, platinum dioxide, or Raney Nickel may be employed. In the hydrogenation carried out in this step, hydrogen atoms are added stereoselectively to the double bond at the 3- and 4-position on the 5-membered ring, and for this reason, the fluorine atom in the fluoroketone derivative (4) may have the desired stereo-configuration.
Steps D and E: The fluoroketone derivative (4) is converted into a hydantoin derivative (5) or an aminocyanide derivative (6), or the like, according to the Strecker Amino Acid Synthesis (Ann., 75, 27 (1850); 91, 349 (1850)), the Bucherer-Bergs Reaction (J. Prakt. Chem., 140, 69 (1934)), or a modified method thereof, followed by hydrolysis, to produce (1S, 2S, 3S, 5R, 6S)- or (1SR, 2SR, 3SR, 5RS, 6SR)-2-amino-3-fluorobicyclo [3.1. 0]hexane-2,6-dicarboxylic acid (7) (in the following, referred to as xe2x80x9cfluorine-containing amino acid derivative (7)xe2x80x9d)
Preferably, the fluoroketone derivative (4) is reacted with sodium cyanide or potassium cyanide and ammonium carbonate in a solvent of alcohols such as ethanol or a mixed solvent of water and an alcohol, preferably for 12 hours to 48 hours at 20xc2x0 C. to 50xc2x0 C., to derive the hydantoin derivative (5) which is a synthesis intermediate. Subsequently, the hydantoin derivative is subjected to hydrolysis by a base such as sodium hydroxide or an acid such as hydrochloric acid, hydrobromic acid, or sulfuric acid, in an inert solvent of, for example, alcohols such as ethanol, ethers such as dioxane, ketones such as acetone, water, or a mixture thereof, to synthesize a fluorine-containing amino acid derivative (7).
In the case where (1SR, 5RS, 6SR)-enone derivative (2) is employed as a starting material, the hydantoin derivative (5) or an aminocyanide derivative (6) synthesized by Steps A, B, C, and D may be optically resolved by the HPLC method employing chiral carriers such as cellulose carbamate derivatives or amylosecarbamate derivatives. In addition, the carboxylic acid derivatives derived by ester hydrolysis of the hydantoin derivative (5) or the aminocyanide derivative (6) synthesized according to Steps A, B, C, and D under the general basic conditions or acidic conditions, and the fluorine-containing amino acid derivative (7) may be optically resolved by the HPLC method employing chiral carriers such as cellulose carbamate derivatives or amylosecarbamate derivatives, or alternatively, may be optically resolved by using optically active amines such as (+)- or (xe2x88x92)-1-phenylethylamine, (+)- or (xe2x88x92)-phenylglycinol, (+)- or (xe2x88x92)-2-amino-1-butanol, (+)- or (xe2x88x92)-alaninol, brucine, cinchonidine, cinchonine, quinine, quinidine, or dehydroabiethylamine.
The fluorine-containing amino acid derivative (7) maybe converted into an ester derivative by protecting the amino group using an appropriate protecting group, subsequently, esterifying the amino-protected derivative using an alkyl halide or an alcohol, according to a common method, and subsequently, removing the protecting group of the amino group. The protection of the amino group, esterification, and deprotection of the amino group are carried out according to the common methods as described in PROTECTIVE GROUPS IN ORGANIC SYNTHESIS (written by THEODORA W. GREENE AND PETER G. M. WUTS), which is incorporated herein by reference. The ester derivative described above does not act on group 2 metabotropic glutamate receptor. However, this ester derivative is subjected to hydrolysis in vivo, converting to the corresponding carboxylic acid which acts on group 2 metabotropic glutamate receptors. As described above, the ester derivative functions as a prodrug, and for this reason, it is an extremely useful compound. The aminocyanide derivative (6), the fluorine-containing amino acid derivative (7), and the ester derivative of the fluorine-containing amino acid derivative (7) obtained by the methods described above may be optically resolved using optically active organic acids such as (+)- or (xe2x88x92)-di-p-toluoyl tartaric acid, (+)- or (xe2x88x92)-dibenzoyl tartaric acid, (+)- or (xe2x88x92)-tartaric acid, (+)- or (xe2x88x92)-mandelic acid, (+)- or (xe2x88x92)-camphoric acid, or (+)- or (xe2x88x92)-camphorsulfonic acid.